The present invention relates to horizontal stabilizer actuators for selectively controlling the operative position of aircraft stabilizers.
Modern aircraft have horizontal stabilizers located at the tail section of the fuselage or the rudder section that are pivotally supported relative to the airplane fuselage to xe2x80x9ctrimxe2x80x9d the aircraft during flight by selective adjustment by the operator or pilot from an internal control unit. This involves adjusting the position of the horizontal stabilizer by a stabilizer actuator to accommodate different load distributions within the aircraft and different atmospheric conditions, i.e. wind, rain, snow, etc. In this regard the stabilizer is traditionally pivotally connected to the rudder section or tail section of the fuselage at a point generally midway along its length. One common trimmable horizontal stabilizer actuator consists of a primary ball nut assembly connected with an actuating drive gimbal which is pivotally connected to one end of the horizontal stabilizer structure. The ball nut assembly includes a ball nut housing and a rotatable ballscrew extending axially and usually vertically through the ball nut housing and a drive gimbal housing. The ball nut housing is connected to the drive gimbal housing by a trunnion segment. The ballscrew, in turn, has its upper end remote from the actuating drive gimbal and is fixed from translation or axial movement by a connection to a second, support gimbal which is pivotally secured to the rudder section or the tail section. As the ballscrew is rotated, the drive gimbal will be moved in translation relative to it. Thus as the ballscrew is rotated in one direction, the leading edge of the horizontal stabilizer is pivoted upward, whereas by rotating the ballscrew in the other direction, the leading edge of the horizontal stabilizer is pivoted downward. Rotation of the ballscrew is routinely done by a motor and associated gearing which is connected to the second, fixed support gimbal and which is actuated by the operator or pilot by the internal control unit. The connection of the stabilizer actuator to the stabilizer is located within the rudder or fuselage tail section and not directly in the air stream.
The horizontal stabilizer movement, as controlled by the operator, is transmitted by the ballscrew through the actuating drive gimbal by way of the primary ball nut assembly which defines a primary load path. The movement has a load with tensile and compressive components as well as a torque component due to the ballscrew thread lead. Failures of the primary load path such as caused by the shearing off of the connecting trunnion segment or by the loss of nut ball members from the ball nut assembly can result in the complete loss of control of the horizontal stabilizer. However, stabilizer actuators have frequently been provided with a secondary load path for alternate control of the stabilizer. In such structures, the primary load path is normally controllably actuated by the operator and is thus under load while the secondary load path is normally unactuated and thus unloaded. In the event of a primary load path failure, the secondary load path is automatically mobilized whereby the stabilizer actuator can continue to be controllably actuated by the operator or pilot by the internal control unit to control the position of the stabilizer. The transition of control to the secondary load path can occur quite rapidly whereby failure of the primary load path is not necessarily detected by the operator or pilot.
However, in the event of a subsequent failure of the secondary load path through continued, periodic use, control of the stabilizer will be completely lost which could result in erratic, oscillatory movement of the stabilizer whereby the ability of the pilot or operator to control the aircraft could be substantially inhibited. This problem is addressed by the present invention.
In the present invention the stabilizer actuator is also provided with a primary and secondary load path. However, in the event of failure of the primary load path, the secondary load path will be automatically actuated to trigger the actuator to a locked condition to hold the horizontal stabilizer in a fixed position. This avoids erratic movement of the stabilizer and hence permits the pilot to regain control through other mechanisms whereby the continued flight and landing of the aircraft can be more readily controlled. Thus the locking, operation of the secondary load path shall be clearly detected by the pilot or operator during the flight by shutting down the drive system and holding the horizontal stabilizer in a fixed, position. Steps can then be taken to repair or replace the stabilizer actuator prior to the next flight. Also, with the present invention it shall be possible to test the condition of the mechanism for the secondary load path to provide permanent immobilization by a readily accessible in-situ inspection structure of the mechanism during routine maintenance checks at periodic intervals. This is to ensure that the secondary load path mechanism is functional. As will be seen, the apparatus for the secondary load path includes a locking mechanism which operates in response to minimal uncontrolled movement of the stabilizer and minimal triggering loads relative to the operating load in response to a failure of the primary load path. Once it is triggered to a locked condition the locking mechanism stays lockingly engaged regardless of varying aerodynamic loads on the stabilizer and hence on the stabilizer actuator and regardless of attempted control of the stabilizer actuator by the operator through the internal control unit. Thus the stabilizer actuator of the present invention provides:
1) permanent immobilization of the stabilizer actuator via a secondary load path to hold the stabilizer in a fixed position in the event of failure of the mechanism for the primary load path;
2) the ability of the locking mechanism for the secondary load path to achieve permanent, fixed immobilization under minimal aerodynamic triggering loads;
3) the ability of the locking mechanism to keep the stabilizer actuator immobilized even though aerodynamic loads of varying magnitudes are applied to the stabilizer up to the tensile and compressive design load limits;
4) a clear signal to the operator, via the locked condition, by rendering the internal control unit ineffective, that there has been a failure in the primary load path and that repair should be done upon landing; and
5) readily accessible in-situ inspection of the locking mechanism for the secondary load path locking function during scheduled intervals to confirm that the locking mechanism should be able to operate when activated after a primary load path failure.
Therefore it is an object of the present invention to provide an aircraft stabilizer actuator which responds in the event of failure of the primary load path to trigger a secondary load path to lock the stabilizer actuator and stabilizer in a fixed position thus inhibiting erratic, uncontrolled movement of the stabilizer.
It is another object of the present invention to provide an aircraft stabilizer actuator which has a primary load path by which the stabilizer is normally selectively actuated by the operator and a secondary load path which will lock the stabilizer actuator to hold the stabilizer in a fixed position in the event of failure of the structure for the primary load path and further providing a means for ready, routine in-situ ground inspection of the secondary load path locking mechanism to periodically determine its operative or inoperative condition.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.